Add the main frame routing ID to WebContentsDelegate, use it in BackgroundContents.

content/public/browser/web_contents.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_H_
 #define CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_H_
 
 #include <set>
 
 #include "base/basictypes.h"
@@ skipping 85 matching lines @@
     // privileged process.
     SiteInstance* site_instance;
 
     // The opener WebContents is the WebContents that initiated this request,
     // if any.
     WebContents* opener;
 
     // If the opener is suppressed, then the new WebContents doesn't hold a
     // reference to its opener.
     bool opener_suppressed;
+
+    // The routing ids of the RenderView and of the main RenderFrame. Either
+    // both must be provided, or both must be MSG_ROUTING_NONE to have the
+    // WebContents make the assignment.
     int routing_id;
     int main_frame_routing_id;
 
     // Initial size of the new WebContent's view. Can be (0, 0) if not needed.
     gfx::Size initial_size;
 
     // True if the contents should be initially hidden.
     bool initially_hidden;
 
     // If non-null then this WebContents will be hosted by a BrowserPlugin.
@@ skipping 488 matching lines @@
 
  private:
   // This interface should only be implemented inside content.
   friend class WebContentsImpl;
   WebContents() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_H_